Influence of Tilt Angle and Probe-Sample Distance on Tissue Diagnosis by Diffuse Reflection Spectra

The use of in vivo optical techniques implies different considerations when compared with measurements made with ex vivo tissues or inert samples. One critical point arises when performing these measurements on volunteers and patients, as slight movements may occur due to involuntary patient reactions or positioning errors made by the practitioner. In this work, diffuse reflectance spectroscopy (DRS) was used with fiber optic probes to evaluate how probe tilt affects spectral information when the probe-sample distance is changed in three biological tissue phantoms. The aim was to determine the maximum allowable error compared to measurements under ideal conditions (no inclination and in contact). Results showed that both variables affect the reflection percentage up to 127% of average percentage of whole spectral error for a combined effect. The effect of introducing a 5° angle is shown to be more pronounced than the variation of sample-probe distance. This fact suggests the need for effective control of the tilt angle in a clinical setting of diagnostic based on DRS.